How could I get with Imagecache a composition of the image itself plus a copy of the image?

I would like to know if there is a way to get with Imagecache and Imagecache actions, or Imagecache and ImageMagick Commands, a composition of the image itself plus a copy of the image with an effect applied, for example a grayscale version.

I´ve discovered a nice technique to get a greyscale version of the image when hovering using jQuery here: Greyscale Hover Effect w/ CSS & jQuery, but what I want is to automatize the creation of the image.

Does anyone have any clue how to achieve this with the Imagecache module?

Thanks!